Common baldness, also known as alopecia, represents the vast majority of all cases of hair loss in humans. The condition is characterized by the gradual loss of hair mostly in men, but also in women. Most current treatments for common baldness are based on the theory that alopecia originates from genetic factors and aging.
Treatments for common baldness include hair transplantation, oral, and topical application of drugs and natural solutions. Hair transplantation methods are usually painful, costly, and frequently result in an undesirable, unnatural appearance. The predominant oral and topical products are pharmaceuticals such as Rogaine® and Regaine® (topical solutions of the drug minoxidil from Upjohn, Inc.), Propecia® and Proscar® (orally ingested tablet of the drug finasteride from Merck and Company, Inc.), Andolactone® (orally ingested tablets or topical solutions of the drug sprionolactone from G. D. Searle, Inc.), Androcur® (orally ingested tablet of the drugs cyproterone acetate and ethinyl estradiol from Schering-Plough, Inc.), Eulexin® (oral tablets of the drug flutamide from Schering-Plough, Inc.). Additionally, oral contraceptives (containing estrogens and/or estradiol), tretinoin, and azelaic acid are drugs that have been the subject of scientific studies for their potential to enhance hair growth. There are also a variety of other products on the market today that claim to aid in the growth of hair. Some of these treatments may have undesirable side effects or may result in recurrence of the condition if application is discontinued.
Hair grows from follicles in the skin that extend from the epidermis (the outmost layer of skin) to the dermis (the deepest layer of the skin). Hair growth is a complex biochemical process that is only partially understood, in part because it is extremely difficult to isolate single hair follicles and grow them in culture medium. However, it is well recognized that hair grows from active hair follicles at a rate of 0.2 to 0.5 millimeters (0.01 to 0.02 inches) per day. Hair growth is not a continuous phenomenon, but rather occurs in cycles of anagen (active growth), catagen (transition to no growth), and telogen (dormancy). A typical anagen phase lasts for 2 to 10 years, after which the cells at the base of the hair follicle enter catagen for about 14 to 21 days. At the end of the catagen phase, the follicle enters the telogen phase, and becomes dormant for a period of 30 to 90 days. During this phase, the previously growing hair detaches from the base of the follicle, and is eventually shed from the skin as it is pushed out of the follicle by the growth of new hair strand that occurs when the follicle enters a new anagen phase.